My daughter's parlor was built from Scott Antes plans and is more or less a single ought. I would be very easy to increase the body size to double ought - what I would suggest is using both the Antes plans and StewMac's (or others) for a 000 and get Martin's dimensions for a 00 - upper and lower bout, lenght, waist, scale length, etc and make your own. the parlor only has one tone bar, I would go with two on an 00.

DaveH
I'm facing the same situation. I bought a 00-21 kit from John Hall. And I don't have a set of plans with dimensions so I can make a mold. So, I'll just draw my own shape based on the dimensions than I can come up with.
After some googling, I came up with many places that give the lower bout width as 14 1/8 in. And one site that gives body length as 19 5/8 and body depth as 4 1/16. But nowhere can I find the upper bout and waist measurements. So I'm extrapolating from the 0 size and 000 size plans that I do have. I will start with an upper bout width of 9 7/8 in. After I make a paper pattern, I'll decide if I like the shape and go from there.
Also, we are making the annual Thanksgiving trip back to Michigan and passing through Lansing for a day. If I can, I'll stop in at Elderly Instruments and measure one of their 00-21's.

Funny you mention Elderly's. I live only about 45 minutes from Lansing (Marshall, MI) and was figuring on the same approach. Not sure they'll be keen with me taking in some paper and tracing the body profile, but being a regular customer maybe it will be OK. I was just there last week to pick up a case for my J-200. It's tough to go there and not spend a lot of money. My son also goes to MSU so I work a quick visit in with the trip.

Aside from the shape and rim dimensions, it would be nice to confirm a bracing pattern. Seems like most use the 000 as reference and work from there.

What tonewood are you using for the S&B? I will probably use EIR as with the current 00-28VS model.

Dave
I used to live in Lansing and worked at Elderly for a while in books and records about 10 years ago. Great place.
My kit from Blues Creek has an all koa body. The bracing is already penciled in, so I'm just going with that. I think that the martin bracing is so standard that it will sound great just as John set it up. The koa is going to make it sound different than a rosewood and spruce model and I plan to do some serious brace scalloping and use light gauge strings. So, it will sound like it sounds and I'll be happy with it.
And now that I think about it, the sides are bent and shaped so the body thickness is a given. I'm not going to change them other than sanding to fit the top.

My first pass CAD extrapolated version of the 0012th fret has an upper bout measurement of 10.21 inches. Tracing the profile and shadowing the brace pattern would be a cool thing to do. Iíll be interested to see how my version compares.

The upper bout and lower bout are sort of in proportion --- how old is this 0021? What is the lower bout measurement? What is the scale length? Just a note -- an OM is not a shape but rather a modification from short to long scale length, at one time almost all shapes and sizes of Martins had/have an "O"rchestra "M"odel. You are correct my version is an extrapolation/down size of the current 000 12th fret and likely a more modern version --- my logic is that builders will esaily be able to use the current 00012th MacRostie drawing for detail reference.

According to 'The Martin Book' by Walter Carter, the 00 shape was first produced in the 1870's. It grew out of the small parlor guitars of that period. The modern 00 came out in the 1930's.
Carter differentiates between the two shapes as the 00 12 fret and the 00 14 fret. I think Martin does, too.
24.9 in. string scale for the 00-21 and the nut width at 1 13/16 in. is even wider than the OM at 1 3/4 and the standard Martin neck is 1 11/16.

The 00-21 is my favorite size and shape. The modern 00's and 000's just don't do it for me.

Not that it really matters and to the credit of the mimf poster, that document has no "documentation" and that is clearly stated. So from an historical stand point if really of no use if cloning is the objective. Measurements from the real deal is the way to go, as mentioned Elderly, Mandolin Brothers, Gurian etc. have those vintage instruments on hand.

I mention this as a reminder that forums can be informative and entertaining but care must be taken choosing the information you plan to act on.

Seems to me there are quite a number of different measurements quoted here. If I were going to try to build a authentic replica, I'd tend to go with the upper bout measurement Dan got at Elderly's. At least, that measurement came from an actual guitar made by Martin.

I am curious about why there are so many different measurements floating around regarding Martin guitars of decades ago. It seems to be the case no matter which model is being discussed. Respected sources seem to vary as well.

I guess there is no real answer but you are correct in that older martins were not held to as tight a tolerance as they are today. There are many list of "exact" sizes of the guitar bodies listed , even at the martin site .
Martin does this by design . So while Martin is as open as any company they still will "protect" their designs. I do work for martin and have to follow the dimensions they give me and they differ from the listings.
I can tell you that of all the old Martins that I have worked on they are withing 1/4 in of the listed sizes. It was in the later 80's that tolerances were pulled tighter in the production floor.
In the old days a jig was used and not all jigs were the exact same so the guitar made with mold # 001 may not be the same shape as the one made in mold #2 etc. The older jigs were made from what was handy at the time and they were all handmade.
I have seen production molds made of Pine , Mahogany , plywood , and some were more worn than others. While this can explain some of the discrepancies you can also look at the production methods of the day. At the time a Guitar was a guitar , so if it looked like a guitar it was . Today tolerances are very tight for a repeatable process . With more modern manufacturing processes you can see how things became more controllable .
I had the honor of getting tracings off all the actual production molds a few years back .
Bill hit it on the head with the last line , The only thing about martins consistency was that there wasn't any until the 80's

For what it's worth..we are in Quartzsite Arizona for a while escaping the cold...lots of musicians here for the winter and I had the chance to measure a Martin 0021 this morning...said to be a 1940 model ...the body length is 19 1/2", the upper bout is 10"...the lower bout is 14 1/4"...the scale length is 24.75...body depth is 3 3/8" at the neck heel and 4 1/4" at the tail block...nut width was 1 7/8" with a string spacing of 2 1/4"..the sound? unbeliveable!!
It belonged to the Man's Father...origional case and except for a neck set...appeared to be otherwise origional. a fair amount of play wear..but beautiful none the less...it had those lovely "Violin lines"!
I was somehow side-tracked and failed to measure the waist...what can I say...DUH?
He said it appraised for $10K...I'm thinkin' that's a bit low..sorry for the rambling.. I couldn't get any pics...he was in the process of leaving and my camera has been missplaced...ughhhh!
Oh well...it was a pleasure seeing and playing this masterpiece...if only for a little while.
Hope this gives some insight! :)

And Bill, if you really want to see differences in measurements, look at what Gibson was doing in the 30's. Heck, some of their guitars had 12. 13 or 14 frets clear, but were still called the same thing (look at the L-0 or L-00 for example)